1. Field of the Invention
The present invention relates to a process for the exploitation of low-grade oxidic and iron-bearing complex ores or concentrates. The invention relates in particular to a process according to which iron-bearing, oxidic complex ores of chromium, aluminum, vanadium, titanium, nickel, manganese and cobalt are exploited.
2. Description of the Prior Art
A corresponding simultaneous exploitation process is not known in the current state of the art, but initial materials which contain several substances to be recovered are treated by several different methods.
Chromium chemicals are usually produced by an oxidizing calcination of a chromite mixture of sodium carbonate/calcium carbonate, whereby sodium chromate is obtained as an intermediate product. However, the use of this process involves several quite serious risks in terms of the environment, health and economy. Such harmful factors include the quality requirements for chromite (SiO.sub.2 concentration must be lower than 1%), the large amounts of gas present during the calcination, the reaction temperature being 1100.degree. C., and a long reaction time, 4 h, as well as a residue which constitutes a problem. Even after a leach, the residue contains chromate of sodium and calcium, which is gradually dissolved by rainwater, unless it is reduced separately.
From vanadium-bearing ilmenite ores, (Fe, V)TiO.sub.3, the vanadium is removed by an oxidizing treatment in the presence of alkali metals. In this case, however, the required amount of alkali is large owing to the alkali-titanium compounds which are formed. In addition, a ferric iron/titanium compound is left as a byproduct; this compound is of little economic value and, owing to its high titanium dioxide content, it is unusable for, for example, the production of raw iron.
The production of ferrochromium from a chromite concentrate or ore is usually carried out in an electric-arc furnace, in which high temperatures have to be used in order to achieve a sufficient reduction rate. In this case it is also necessary to add suitable additives for controlling the melting point and viscosity of the slag, and thus a large amount of feed mixture must be smelted at a high temperature. The amount of electric energy per one tonne of ferrochromium is high, since the required temperatures are 1550.degree.-1600.degree. C. for the metal and 1650.degree.-1700.degree. C. for the slag. Furthermore, the slag thereby obtained is usually waste material or suitable only for purposes of little value, since because of fluxing the melting point of the slag is lowered and thereby the refractory quality of the bricks or mixes possibly made from the slag is lowered. The process has a further disadvantage in that the coke used as a reductant must be of a high quality. High-quality coke is difficult to obtain, and furthermore, its price is high.
The treatment of an aluminum oxide-bearing laterite in order to form pure alumina, Al.sub.2 O.sub.3, is carried out using the Bayer or the Pedersen process. The disadvantage of the Bayer process is that laterite in which the proportion of hematite is high and the proportion of aluminum oxide respectively low cannot be used in the process. In addition, an iron-bearing red mud is produced in the Bayer process, and this red mud is difficult and expensive to dispose of. The disadvantage of the Pedersen process is that the consumption of energy in the electric-furnace smelting of the process is high, since the lime has to be fed in as limestone, or it has to be calcinated separately before the smelting.